1. Field of the Invention
This invention relates to a light emitting and receiving device for bidirectional optical communications with one optical fiber.
2. Description of the Related Art
FIG. 5 is a basic block diagram of an optical bidirectional communications system proposed in Japanese Patent Application Unexamined Publication No. 61-9610. Below is description of the system construction.
Denoted 101 is a light emitting and receiving device which consists of a light emitter 102 for converting electrical signals to optical signals, a light receiver 103 for converting optical signals to electrical signals, and an optical branching filter 104. Denoted 105 is also a light emitting and receiving device which consists of a light emitter 106, a light receiver 107 and an optical branching filter 108, all having the same constructions as those in the light emitting and receiving device 101. The light emitting and receiving devices 101 and 105 are optically connected to each other via one optical fiber 109.
The publication as mentioned above also discloses a light emitting and receiving device 101xe2x80x2, 105xe2x80x2 which is of one-piece structure as shown in FIG. 6. In this structure, light from a light emitting element 110 is converted into parallel lights at a lens 111, gathered via a half mirror 112 at a lens 113, and passed to an optical fiber 114. On the other hand, light from the optical fiber 114 is reflected at the half mirror 112, gathered at a lens 115, and passed to a light receiving element 116.
The publication as mentioned above further discloses a light emitting and receiving device 101xe2x80x3, 105xe2x80x3 as shown in FIG. 7, which consists of a light emitting element 117, an optical fiber 118, a first lens 119, a glass block 120, a second lens 121 and a light receiving element 122.
The optical fiber 118 has its front end portion received at a center axis in a glass tube 123 and has its front end surface obliquely ground at an angle of about 45xc2x0 with the glass tube 123.
The first lens 119 is disposed between the light emitting element 117 and the optical fiber 118 and gathers light from the light emitting element 117 to pass to the optical fiber 118.
The glass block 120 has a surface 120a in opposition to an end surface of the first lens 119, which is ground at right angles to the center axis of the optical fiber 118, and a surface 120b ground at an angle of about 45xc2x0 relative to the center axis of the optical fiber 118 and coated with a half mirror 124.
The second lens 121 gathers light from the optical fiber 118 which is reflected at the half mirror 124.
A holder 126, which has the glass tube 123 and an outer sheath 125 of the optical fiber 118 fixed in its hollow interior, the light emitting element 117, the first and second lenses 119 and 121, the light receiving element 122 and the glass block 120 are received in a housing 127.
Another system is also proposed in Japanese Patent Application Unexamined Publication No. 63-175539, which is as shown in FIG. 8.
In this system, as shown in FIG. 8, light emitted from a light emitting means 129 of a light emitting and receiving device 128 passes through a half mirror 130, enter and travel through an optical fiber 131, is reflected at a half mirror 133 of a light emitting and receiving device 132, and pass through a diffraction grating 134 into a light receiving means 135.
Description of the operation in the opposite direction will be omitted. Denoted 136 is a light receiving means and 137 is a light emitting means.
With the above systems, however, because each light emitting and receiving device is provided with a half mirror as an indispensable component, loss of optical power has been inevitable. In other words, if light passes through a half mirror in optical communications, its amount becomes one half the amount before passing through (reflection at) the half mirror, resulting in the loss mentioned above.
Further, because of the structure in which the light receiving means receives light after it is reflected at the half mirror, it is necessary that the receiving means is situated at a position perpendicular to the axis of the optical fiber, the light emitting and receiving device becomes unfavorably upsized.
This invention has been accomplished to overcome the above drawbacks and an object of this invention is to provide a light emitting and receiving device which reduces loss of optical power, and which is downsized.
In order to attain the object, according to this invention, there is provided a light emitting and receiving device which comprises: an optical fiber; a light propagating member capable of propagating light therethrough, which is provided with a light emitting means, the light emitting means converting first electrical signals into first optical signals; and a light receiving means which receives second optical signals and converts the second optical signals into second electrical signals, the light receiving means being disposed coaxially with the optical fiber, wherein the light propagating member is situated between an end of the optical fiber and the light receiving means, such that the light emitting means emits the first optical signals into the optical fiber at the end, and that the light propagating member receives from the optical fiber and propagates therethrough the second optical signals to the light receiving means.
In the above light emitting and receiving device, due to the arrangement in which the light propagating member with the light emitting means is situated between an end of the optical fiber and the light receiving means, the light having traveled through the optical fiber passes through the light propagating member to the light receiving means, and the light emitted from the light emitting means passes through the light propagating member or directly into the optical fiber.
Without a half mirror which has conventionally been used as an indispensable component, in the present device, for example the light from the optical fiber is prevented from being reduced by half, thereby to realize a better optical communication.
Further, due to the arrangement in which the light receiving means is disposed coaxially with the optical fiber and the light emitting means is provided on the light propagating member between the light receiving means and the optical fiber, a more compact light emitting and receiving device than the conventional one is attained. In other words, because no half mirror is employed which reflects light, no main component needs to be located at a position in a direction of reflection of light from the half mirror or direction perpendicular to the axis of the optical fiber, a compact light emitting and receiving device is attained.
Thus, loss of optical power is suppressed, while attaining a downsized light emitting and receiving device.
Incidentally, during propagation of light through the light propagating member to the light receiving means, part of the light may be obstructed by the light emitting means. This, however, can be coped with by reducing the surface area of the light emitting means facing the optical fiber. The loss can be minimized in this way and will cause no problem.
Preferably, the light propagating member has a cavity formed therein for mounting the light emitting means in an integrated manner with the light propagating member.
In this way, the light emitting means may be prepared in advance, in a separate process, in conformity to the shape of the cavity and combined integrally with the light propagating member by mounting same in the cavity.
Preferably, the cavity is formed at such position as to open to an end surface of the light propagating member opposed to the end of the optical fiber.
This arrangement allows the light from the light emitting means to directly enter the optical fiber, while reducing the number of boundary surfaces between the light emitting means and the light propagating member.
Preferably, the light emitting means, when mounted in the cavity, has an end surface thereof flush with the end surface of the light propagating member.
Advantageously, the light propagating member has a step portion formed at an end thereof opposed to the end of the optical fiber for mounting the light emitting means in an integrated manner with the light propagating member, the step portion extending in a width direction across the light propagating member.
This arrangement allows the light emitting means to be prepared in advance, in a separate process, in conformity to the shape of the step portion and to be combined integrally with the light propagating member by mounting same in the cavity. This arrangement also allows the light from the light emitting means to directly enter the optical fiber, while reducing the number of boundary surfaces between the light emitting means and the light propagating member. The step portion is easily formable in the light propagating member.
Preferably, the light emitting means comprises a light propagating portion having the same refractive index as that of the light propagating member.
According to this invention, there is further provided an optical connector including a receptacle and an optical plug, the receptacle having a housing and a light emitting and receiving device received in the housing, the optical plug having a plug housing and an optical fiber received in the plug housing to be urged to the light emitting and receiving device when the receptacle and the optical plug are fitted together, the light emitting and receiving device comprising: a light propagating member capable of propagating light therethrough, which is provided with a light emitting means, the light emitting means converting first electrical signals into first optical signals; and a light receiving means which receives second optical signals and converts the second optical signals into second electrical signals, the light receiving means being disposed coaxially with the optical fiber, wherein the light propagating member is situated between an end of the optical fiber and the light receiving means, such that the light emitting means emits the first optical signals into the optical fiber at the end, and that the light propagating member receives from the optical fiber and propagates therethrough the second optical signals to the light receiving means.
The above and other objects, features and advantages of this invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings.